Such green sheets, before being fired, must often be provided with a number of holes; the number and position of the holes, or in other words the hole pattern, must be changed from time to time or even from one piece to another. Tools with a plurality of movably supported dies are therefore known, of which only one selected group of dies at a time executes a stamping operation.
From U.S. Pat. No. 5,024,127, a stamping tool with a plurality of dies, each of which is assigned its own magnet coil drive mechanism, is known for the purpose. By supplying current to the respective magnet coil, the die connected to it is made to execute an axial motion and thus a stamping operation.
The installation space required for the coils defines a minimum die spacing of adjacent dies. This spacing cannot be made narrower arbitrarily. Moreover, such tools require cooling, because of the lost heat occurring in the coil drive mechanisms.
For stamping variable hole patterns in metal sheets, German Patent Disclosure DE 41 35 787 A1 discloses a stamping machining device that has a lower tool with a cutting plate and an upper tool with axially movably supported dies. The upper tool is secured to the tappet of a press and in operation executes a vertically reciprocating motion. Each die is assigned a locking bar, disposed above its head and supported movably transversely to it, which can lock the die in its axial position or release it. Each locking bar is connected to the piston rod of a separate pneumatic actuator, which is seated on the outside of the upper tool.
The attainable pitch spacings here are dependent on the size of the pneumatic actuators.